The present invention relates to an oxygen scavenger, and more particularly to an oxygen scavenger which can effectively remove dissolved oxygen in water and, in particular, is useful in inhibiting the corrosion in a boiler system by removing dissolved oxygen in feed water.
Dissolved oxygen in feed water is a factor causing corrosion in a boiler system including a boiler, a heat exchanger and an economizer arranged upstream of the boiler, and a steam and condensate return line arranged downstream of the boiler. To inhibit the corrosion in the boiler system, dissolved oxygen in feed water should be removed by deoxidizing treatment of the feed water of the boiler.
Conventionally, chemical treatment or physical treatment has been applied for the removal of dissolved oxygen. As for the chemical treatment, a method of adding an oxygen scavenger, such as hydrazine (N2H4), sodium sulfite (Na2SO3), or hydroxylamine, into the feed water has been widely employed. However, hydrazine may be harmful to human health.
Since a reaction between sodium sulfite and oxygen is too rapid, sodium sulfite dissolved in water and stored in a tank reacts with oxygen in air before it is added in feed water, thereby reducing the concentration of effective component thereof. Therefore, there is a problem that sodium sulfite sometimes does not produce sufficient effect of dissolved oxygen removal. Since the feed water treated with sodium sulfite contains sulphate ion as a reaction product of the sodium sulfite and oxygen, there is a problem that the sulphate ion becomes another factor causing the corrosion and scale in a boiler system.
There is also a problem that hydroxylamine generates acid such as nitric acid when the hydroxylamine is added in feed water and reacts with oxygen in the boiler, thereby reducing corrosion inhibition effect for the boiler.
As an oxygen scavenger other than the above, a heterocyclic compound with N-substituted amino group such as 1-aminopyrrolidine and 1-amino-4-methylpiperazine has been proposed (Japanese patent H10-158872A). The heterocyclic compound with N-substituted amino group exhibits excellent oxygen scavenging effect by reacting with dissolved oxygen in feed water, thereby exhibiting excellent effect of inhibiting the corrosion in a boiler system.
However, the heterocyclic compound with N-substituted amino group is not entirely satisfactory as an oxygen scavenger under all conditions because at relatively low water temperatures, e.g. 80xc2x0 C. or lower, its reaction with dissolved oxygen is rather slow so that the oxygen scavenging effect may be insufficient.
The use of a hydroxybenzene derivative together with the heterocyclic compound with N-substituted amino group speeds up the reaction with dissolved oxygen, thus improving the corrosion inhibition effect at relatively low water temperatures (Japanese patent H10-323561A). However, since most of hydroxybenzene derivatives are not water soluble and even water soluble hydroxybenzene derivative has low solubility, it is impossible to dissolve the hydroxybenzene derivative sufficiently for exhibiting effect.
It is the object of the present invention to solve the aforementioned problems and to provide an oxygen scavenger which contains heterocyclic compound with N-substituted amino group as an effective component and can adequately exhibit the oxygen scavenging effect in not only feed water lines for high temperature water, a boiler, and steam and condensate return lines, but also feed water lines for low temperature water.
An oxygen scavenger of the present invention contains a heterocyclic compound with N-substituted amino group and/or a salt thereof; one or more aromatic compound selected from a group consisting of hydroxybenzene derivatives and naphthoquinone derivatives; and neutral amine.
In the oxygen scavenger of the present invention, the heterocyclic compound with N-substituted amino group or the salt thereof can exhibit excellent oxygen scavenging effect even in feed water lines containing low temperature water because of a catalytic function of the hydroxybenzene derivative and/or the naphthoquinone derivative which can coexist under the presence of the neutral amine. By adding the neutral amine, such chemical of one-pack type that can provide well effect for inhibiting corrosion of all of pipes in a feed water system, a boiler, and steam and condensate return lines can be provided.
In the present invention, examples of the hydroxybenzene derivatives are represented by the following formulas i and ii, and examples of naphthoquinone derivatives are represented by the following formulas iii and iv: 
where R1 is xe2x80x94OH,
R2 is xe2x80x94OH or xe2x80x94NH2,
R3 and R4 each designate xe2x80x94OH, xe2x80x94NH2 lower alkyl group having 1-8 carbon atoms, carboxyl group, or lower alkoxy carbonyl group,
R5 and R6 are each xe2x80x94OH or xe2x95x90O, and
R7, R8,R9, and R10 each designate xe2x80x94OH, xe2x80x94NH2 lower alkyl group having 1-8 carbon atoms.